JP2004316657A - Mixed adjusting type hybrid bucket, and its relating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the total weight of a bucket by maximum about 30% by a hybrid bucket, to reduce the mounting stress and to enhance the reliability without changing any aerodynamic characteristic of a blade-shaped portion. <P>SOLUTION: A steam turbine rotor wheel includes a plurality of buckets (10 and 34), each of which has a shank portion (12) and a blade-shaped portion (14) and is fixed around a circumferential part of the wheel, and a plurality of buckets include two groups of buckets (10 and 34) having predetermined resonance frequencies different from each other. A method for reducing the vibration in the bucket row on the steam turbine rotor wheel includes (a) a step of preparing the bucket (10) of the first group having the first predetermined natural frequency range, (b) a step of preparing the bucket (34) of the second group having the second predetermined natural frequency range different from the first predetermined natural frequency range, and (c) a step of assembling the bucket out of the buckets in the first and second groups on the rotor wheel in an alternate manner. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates generally to steam turbine buckets (or blades), and more particularly to composite buckets having different predetermined frequency damping characteristics and tuned to provide improved system damping.

  Steam turbine buckets operate in environments subject to large centrifugal loads and oscillating stresses. The vibration stress increases when the natural frequency of the bucket reaches a resonance state. The magnitude of the vibration stress when the bucket vibrates in resonance is proportional to the amount of damping (damping consists of material, aerodynamic and mechanical elements) and the vibration excitation level existing in the system. In the case of continuously coupled buckets, the vibration frequency is a function of the overall system of blades in the row, not necessarily of the individual blades in the row.

  At the same time, the centrifugal load is a function of operating speed, bucket mass and radius from the engine centerline where the mass is located. As the bucket load (mass) increases, the physical area or cross-section is reduced to a lower radial height to allow the mass to be supported on the bucket without exceeding the allowable stress in a given material. Must be increased in Increasing the cross-sectional area of the bucket at this lower span will result in excessive obstruction of the flow at the root, thus reducing performance. Bucket weight contributes to greater disk stress and can therefore reduce reliability.

Several prior U.S. patents relate to so-called "hybrid" bucket designs in which a portion of the airfoil is comprised of a combination of metal and polymer filler. These prior patents include U.S. Pat. Nos. 6,086,098, 6,069,086, and 6,098,045.
JP-A-10-54204 U.S. Patent No. 6,042,338 US Patent No. 5,931,641 JP-A-9-303104

  The present invention proposes a means of suppressing the aeroelastic response of a bucket or blade row (continuously coupled or free standing) by mixing and adjusting the natural frequencies of the blades or buckets in the row. Specifically, this patent utilizes the concept of a hybrid bucket as disclosed in U.S. Pat. No. 5,931,641 but uses an internal pocket configuration within the airfoil portion of the bucket. Extending the concept to include optimizing, in an exemplary embodiment, different internal ribs and / or pockets, each having the same external aerodynamic shape and profile, but resulting in different bucket resonance frequencies It is intended to form two groups or groups of buckets with shapes. The pockets inside the airfoil portion of the bucket are preferably filled with a polymer filler, which also forms one surface of the bucket airfoil. By intentionally altering the natural frequencies of the two groups of buckets, the bucket damps this natural difference in natural resonance frequencies without adversely affecting the aerodynamic characteristics of the bucket, and the system response to synchronous and asynchronous speed oscillations. Can be purposely and logically assembled for use as a means of doing so.

  In this exemplary embodiment, two groups or sets of buckets having different internal pocket configurations along the pressure side of the bucket are assembled on a steam turbine rotor wheel in a single row of buckets. One group of buckets is designed to have a higher resonant frequency than another group of buckets. Once the bucket configuration has been determined, the buckets are assembled on the wheel in a pattern that best achieves the goal of vibration suppression. In this exemplary embodiment, the buckets of each group are assembled on a wheel in an alternating fashion, i.e., with each bucket of one group adjacent to another group of buckets. However, other arrangements still within the scope of the present invention are conceivable.

  The hybrid bucket can achieve up to about a 30% reduction in the overall weight of the bucket, thereby reducing mounting stress and improving reliability without changing the aerodynamic characteristics of the airfoil.

  Accordingly, in a broader aspect, the present invention relates to a steam turbine rotor wheel, the steam turbine rotor wheel including a plurality of buckets fixed about a circumferential periphery of the wheel, each bucket comprising a shank portion and a blade. And the plurality of buckets include two groups of buckets each having a different predetermined natural resonance frequency.

  In another aspect, the invention relates to a steam turbine rotor wheel, the steam turbine rotor wheel including a row of buckets fixed about a circumferential periphery of the wheel, the bucket rows alternating around a periphery of the wheel. It includes two groups of buckets arranged in a pattern, each group having individual means for reducing the amplitude of vibration of the bucket train.

  In another aspect, the invention is directed to a method of reducing vibration in a row of buckets on a steam turbine rotor wheel, the method comprising the steps of: a) providing a first group of buckets having a first predetermined natural frequency range; Providing; b) preparing a second group of buckets having a second predetermined natural frequency range different from the first predetermined natural frequency range; and c) first and second groups. Assembling the buckets on the rotor wheel in an alternating manner.

  The present invention will now be described in detail with reference to the drawings specified below.

  FIG. 1 shows a steam turbine bucket 10 in a partially manufactured form. Bucket 10 includes a shank portion 12 and an airfoil portion 14. The present invention relates to an airfoil preferably made of steel or titanium, but other suitable materials include aluminum, cobalt or nickel. Ribs 16,18 are cast integrally with the airfoil to form individual pockets 20,22,24. However, it will be appreciated that the ribs do not extend flush with the side edges 26, 28 of the airfoil. In practice, the rib height can be different depending on the particular application. A polymer-based filler 30 as described in US Pat. No. 5,931,641 is molded into place on the pressure side of the airfoil, as shown in FIG. And 24 and cover the ribs, thereby forming a smooth surface 32 on the pressure side of the bucket. In particular, the filler 30 can consist essentially of an elastomer such as poly (dimethylsiloxane). Other suitable options for elastomers include, but are not limited to, poly (diphenyldimethylsiloxane), poly (fluorosiloxane), Viton ™, polysulfide, poly (thiol ether), and poly (phosphazene). It is.

  Options for bonding the filler 30 to the metal surface of the airfoil include, but are not limited to, self-adhesion, adhesion between the filler 30 and the metal surface of the airfoil, tackiness (tacky). Film or paste) and fusion.

  When an elastomer is used as the filler, the elastomer has an average modulus of approximately 250 psi (pounds per square inch) to approximately 50,000 psi (and more preferably approximately 250 psi to approximately 20,000 psi) over the operating temperature range. It is further noted that is preferred. Elastomers that are too soft (i.e., having an average modulus of less than about 250 psi) are structurally unable to form an airfoil shape and are too hard (i.e., have an average modulus of greater than about 50,000 psi). ) Elastomers cannot be manufactured to the required close tolerances. A more preferred range for the average modulus is from about 500 psi to about 15,000 psi. In some applications, a conventional thin film (not shown) and a conventional corrosion-resistant coating (not shown) may cover the exposed surface of the bucket airfoil 14.

  In the embodiments described above, the ribs 16, 18 are illustrated as inclined in opposite directions along the length of the airfoil portion 14, but other arrangements are also within the scope of the invention.

  Turning to FIG. 3, another bucket 34 shown includes a more complex set of ribs 36, 38, 40, 42, 44, 46 and connecting web portions 48, 50. The ribs are concentrated near the radial center of the airfoil and correspondingly form a greater number of pockets. However, once the filler 30 is molded in place, the bucket 34 will otherwise have the same appearance as the bucket 10 shown in FIG.

  Turning now to FIG. 4, yet another embodiment of the adjusted bucket is shown. Here, the bucket 52 is formed without ribs, or more appropriately with a single large pocket 54, and the entire pocket will be filled with the polymer-based filler 30. .

  In an exemplary embodiment, the bucket design described above can be used to form a row of buckets on a steam turbine rotor wheel 56 as shown in FIG. Specifically, groups A and B (each comprising, for example, buckets 10 and 34, respectively) are arranged in an alternating manner, ie, ABAB. . . In a pattern such that one group of buckets is always adjacent to the other group of buckets. Buckets A, B can also have internal pocket configurations other than those described herein to produce the desired vibration frequency difference. Again, it is possible to change the pattern of the bucket group distribution to obtain the desired vibration damping characteristics. For example, the pattern AABBAA. . . Etc. can also be used.

  In particular, the present invention designs one group of buckets with equal natural frequencies between two "per revolution" references (eg, 4 divisions per revolution and 5 divisions per revolution), and Design another group of buckets with different rib or pocket configurations so that the natural frequencies are equal for a set of "per revolution" stimuli (eg, 3 divisions per revolution and 4 divisions per revolution) There is a possibility to do. Analysis results have shown that the natural frequency of the bucket can be changed significantly (± 10% or more) by changing the internal rib configuration and / or pocket shape.

  Thus, the present invention allows blades to be manufactured to specifically obtain different natural frequencies, rather than selecting based on the "as-manufactured" natural frequencies. Coordinating the individual natural frequencies of the buckets reduces the vibration amplitude of the entire row of blades by damping the system response to synchronous and asynchronous vibrations without adversely affecting the aerodynamic characteristics of the blade design.

  Another important consideration is the reduction in mass made possible by using a polymer-based filler 30. For example, in the case of a blade configured as a whole as shown in FIGS. 1 and 3, the bucket weight can be reduced by about 30%. Such weight reduction reduces mounting stresses without changing the aerodynamic configuration of the airfoil, thereby improving reliability. The low cycle fatigue life is improved and the risk of stress corrosion cracking can be reduced.

  Although the present invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, the present invention is not limited to the disclosed embodiments, and is not limited to the claims. Is for the sake of easy understanding and does not limit the technical scope of the invention to the embodiments.

1 is a perspective view of a partially manufactured bucket according to the present invention. FIG. 2 is a perspective view of the bucket shown in FIG. 1 after a polymer filler has been added to the bucket. FIG. 4 is a perspective view of a partially completed bucket showing another configuration according to the invention. FIG. 4 is a perspective view of a partially completed bucket showing yet another configuration according to the present invention. The axial schematic front view of the turbine wheel provided with the attached bucket.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 10 Steam turbine bucket 12 Shank part 14 Airfoil part 16, 18 Rib 20, 22, 24 Pocket 26, 28 Side edge of airfoil part

Claims (10)

A plurality of buckets (10, 34) fixed around the circumference of the wheel, each bucket (10) including a shank portion (12) and an airfoil portion (14), wherein the plurality of buckets A steam turbine rotor wheel (56) comprising two groups of buckets (10, 34), each having a different predetermined resonant frequency. One group of buckets (10) alternates with the other group of buckets (34) around the periphery of the wheel, and every bucket of the one group is adjacent to the other group of buckets. The steam turbine rotor wheel of claim 1. The steam turbine rotor wheel of any preceding claim, wherein said airfoil (14) is comprised of a metal and a polymer filler (30). The polymer filler (30) consists essentially of poly (dimethylsiloxane), poly (diphenyldimethylsiloxane), poly (fluorosiloxane), Viton ™, polysulfide, poly (thiol ether) and poly (phosphazene). The steam turbine rotor wheel according to claim 3, wherein the wheel is selected from the group. The steam turbine rotor wheel of any preceding claim, wherein the polymer filler (30) has an average modulus of 250 psi to 50,000 psi. The steam turbine rotor wheel of any preceding claim, wherein the polymer filler (30) has an average modulus of 250 psi to 20,000 psi. The steam turbine rotor wheel of any of the preceding claims, wherein the polymer filler (30) has an average modulus of between 500 psi and 15,000 psi. A method for reducing vibration in a bucket train on a steam turbine rotor wheel, comprising:
a) providing a first group of buckets (10) having a first predetermined natural frequency range;
b) preparing a second group of buckets (34) having a second predetermined natural frequency range different from said first predetermined natural frequency range; and c) said first and second natural frequency ranges. Assembling the buckets of the buckets of the group on the rotor wheel in an alternating manner;
A method that includes The first and second predetermined natural frequency ranges correspond to different rib arrangements (16, 18) (36, 38) in respective airfoil portions of the first and second groups of buckets (10, 34). , 40, 42, 44, 46). The rib arrangement (16, 18) forms a pocket (20, 22, 24) inside the airfoil portion, and the method further comprises the step of filling the pocket with a polymer filler (30). The method of claim 9 comprising:

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